Pneumatic conveying systems for transporting material through a conduit have been in use for years and are well known in the art. Over the years the designs of these systems have changed to provide for greater efficiency in operational cost and labor. For instance, early systems utilized belt driven conveyors to transport materials from an input hopper to a mixing chamber. Unfortunately, these systems were inefficient in that the belt drives experienced many problems, such as wearing and breakage. Due, in part to problems experienced with belt systems, pneumatic conveying systems were developed.
Generally, pneumatic conveying systems include a feed mechanism, such as, an auger, for transporting the material to a mixing chamber. In the mixing chamber, the material is entrained in pressurized air which is supplied into the mixing chamber through jets or air inlets. In some systems, the material and air are mixed and accelerated in an accelerating device, such as, a venturi pipe, which is connected to the mixing chamber. The accelerated mixture is then transported out of the venturi pipe and into a conduit which conveys the materials to a specified destination. Typically, conventional pneumatic conveying systems can transport material up to about 1,000 feet. The limited distance the material can be conveyed is due, in part, to the operating pressure of the system and the instability of the material flow in the conduit.
Many other problems also exist with pneumatic conveying systems. For example, if excessive pressure builds up in the conduit, e.g., from a blockage in the conduit, gas and product back flow into the hopper. This back flow is known as "blowback". Further, as the material travels through the conveying conduit, in earlier designs, and current designs, it strikes the walls of the conduit. This not only damages the walls of the conduit, but damages the material as well. Thus, problems of erosion of equipment and attrition of product are also present. Finally, many current designs incur a high cost of operation due to the high requirement of energy input to operate the system.
Many pneumatic systems have been developed to address different problems. For instance, the blowback problem, among others, was addressed in the system described in U.S. Pat. No. 4,711,607 to Wynosky et al. In the Wynosky device, a rotating auger enclosed by a cylindrical barrel transports particulate material towards the discharge end of the barrel which resides within a plenum chamber. Pressurized gas is introduced into the plenum chamber for creating a gas flow in a venturi pipe, which is coupled at one end to the plenum chamber and at its other end to a conduit used to transport the material. Measurements of the pressure differential between the plenum chamber and the conduit are used to monitor potential blowback problems. Further, this system operates at lower operating pressures than most systems, e.g., 12-15 psi. Nonetheless, this system does not achieve a sufficiently stable flow of material through the conduit, which restricts the distance over which the material can be transported, including the ability to transport the material through elevational or directional changes.
U.S. Pat. No. 5,681,132 to Sheppard, Jr. describes an on-line pumping unit designed to extend transport distances. In Sheppard, the pumping unit includes a screw conveyor assembly coupled to a laminar flow, inductor assembly. In this system, the inductor assembly forms the core of a linear accelerator apparatus used to extend transport distances. Nonetheless, this system does not teach how material can be conveyed over very long distances, such as, for example, a mile.
As shown from above, a need exists in the art for a system that requires low energy input, reduces equipment wear, reduces product degradation and can transport materials for long distances, such as, a mile. Further, a need exists for a system that can convey materials through dramatic high angle and vertical elevation and sharp directional changes. A need also exists for a system that can convey materials without plugging, and can further classify and mechanically dry materials during processing.